Barc-assisted process for planar recessing or removing  of variable-height layers

ABSTRACT

An IC device manufacturing process effectuates a planar recessing of material that initially varies in height across a substrate. The method includes forming a bottom anti-reflective coating (BARC), baking to induce cross-linking in the BARC, CMP to remove a first portion of the BARC and form a planar surface, then plasma etching to effectuate a planar recessing of the BARC. The plasma etching can have a low selectivity between the BARC and the material being recessed, whereby the BARC and the material are recessed simultaneously. Any of the material above a certain height is removed. Structures that are substantially below that certain height can be protected from contamination and left intact. The method can be particularly effective when an abrasive used during CMP forms ester linkages with the BARC.

BACKGROUND

The present disclosure relates to integrated circuit (IC) device manufacturing processes especially replacement gate processes.

In an effort to increase device densities, many years of research have been devoted to reducing critical dimensions (CDs) in semiconductor devices. This research has led to a long felt need to replace traditional gate materials with high-k dielectrics and metal gates. High-k dielectrics can provide enhanced capacitance in comparison to an equivalent thickness of silicon dioxide. Metal electrodes with suitable work functions can avoid charge carrier depletion proximate the electrode interface with the high-k dielectric. The electrodes for P-channel and N-channel transistors generally require different metals.

Suitable metals for gate electrodes can be adversely affected by processing used to form source and drain regions. In particular, annealing can cause an undesirable shift in the work function of electrode metals. This has led to the development of various new processes, including replacement gate (gate-last) processes. In a replacement gate process, a dummy gate stack is formed, which is a gate stack formed using polysilicon in place of metals. After source and drain regions are formed, the polysilicon is removed to form trenches which are then filled with the desired metals.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flow chart of an integrated circuit device manufacturing process in accordance with some embodiments.

FIGS. 2-6 illustrate a partially manufactured integrated circuit device undergoing processing in accordance with some embodiments of the process illustrated by FIG. 1.

FIG. 7 is a flow chart of an integrated circuit device manufacturing process in accordance with some embodiments.

FIGS. 8-13 illustrate a partially manufactured integrated circuit device undergoing processing in accordance with some embodiments of the process illustrated by FIG. 7.

FIG. 14 is a flow chart of an integrated circuit device manufacturing process in accordance with some embodiments.

FIGS. 15-39 illustrate a partially manufactured integrated circuit device undergoing processing in accordance with some embodiments of the process illustrated by FIG. 14.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Optimizing integrated circuit designs to make efficient use of chip area, minimize power requirements, and maximize speed often results in designs featuring a mixture of transistor types including N-channel and P-channel, standard voltage and low voltage, and long channel and short channel. This mixture of types, and the variation in pattern density across the chip surface, result in variations in thickness and height in various material layers formed over the course of integrated circuit device manufacturing. These variations are particularly difficult to manage in replacement gate processes where the thicknesses of some layers can be affected by the height or depth to which a removal process has recessed a previously deposited layer.

The present disclosure provides processes that effect a planar recessing of a topographically variable material over a substrate surface. Topographically variable means that the material varies in height across the substrate. The verb “recess” is used herein to mean to cause to recede by removing an outer or uppermost portion. Recessing does not require that the material be lowered past another material or indented. Planar recessing means that the material is recessed to an approximately planar surface, whereby any of the material above the plane is substantially removed and any of the material below the plane is left substantially intact. In some embodiments, the removal is top-down meaning the removal is sequential from highest over the substrate to lowest with the removal front corresponding approximately with a plane descending toward the substrate surface. In some embodiments, the material is removed completely. In some embodiments, the material is removed from the surface of another material, which is a material that is susceptible to damage or is made non-planar by chemical mechanical polishing (CMP). In some embodiments, the topographically variable material is recessed to within a target range for height. In some embodiments, the material is recessed within another material that is substantially unaffected by the recessing process. In some embodiment, a plurality of topographically variable materials are recessed simultaneously.

FIG. 1 provides an example process 100 in accordance with some embodiments of the present disclosure. FIGS. 2-6 illustrate an example integrated circuit device 200 undergoing process 100. Process 100 includes action 101, which is initial processing that produces topographically variable layers 207A and 207B as shown in FIG. 2. Process 100 includes a series of actions 110 that form a uniformly recessed bottom anti-reflective coating (BARC) 209 and effectuate a planar recessing or removal of layer 207A or 207B.

As shown in FIG. 2, layers 207 (layers 207A and 207B collectively) are formed over a substrate 201, a layer 203, and a layer 205. Layer 203 is an example of a material that would be damaged by CMP or that does not planarizes well under CMP. Layer 205 is an example of a material that can be left substantially unaffected by recessing processing 110 and within which layers 207 can be recessed. In some embodiments, substrate 201 includes fins 247.

Initially, both layer 207A and layer 207B are at height 206A over substrate 201. In this example, the height of substrate 201 is represented by the line S-S′, which is at the base of fins 247. It should be appreciated that the height of substrate 201 is merely a reference plane for defining heights and that the plane identified with the line S-S′ is only one example of a suitable reference plane. A plane through the tops of fins 247 could also provide a suitable reference plane. In most embodiments, substrate 201 is a wafer. A plane through the center of the wafer, or on a face of the wafer at some point in processing, could also provide a suitable reference plane.

The surface of device 200 including layers 207 has gaps 208. In some embodiments, a layer 207 that is to be made to recess has a pattern density that varies across substrate 201. In some embodiments, a layer 207 has a pattern density that varies with height continuously or in multiple steps between its density in the plane A-A′, which is at the initial height 206A of layers 207, and its density in the plane B-B′, which is at the lower, target height 206B for layers 207. Variations in pattern density across substrate 201, variation in pattern density with height, and gaps 208 are challenges to recessing a layer 207 in a planar fashion. Processes provided by the present disclosure are suited to meeting those challenges.

Layers 207 can be any of a wide variety of materials. In some embodiments, a layer 207 is a hard mask material. In some embodiments, a layer 207 is a metal. These materials can be more difficult to recess in a planar fashion than some other materials.

Processing 110 begins with act 111, filling gaps 208 and coating layers 207 with a polymeric bottom anti-reflective coating (BARC) 209 as shown in FIG. 3. In some embodiments, BARC 209 is formed by spin coating substrate 201 with a solution containing monomers and initiating polymerization. In some embodiments, BARC 209 is formed to a thickness in the range from 300 to 5000 Å. In some embodiments, BARC 209 fills at least 98% of the space in gaps 208.

Processing 110 continues with act 113, baking that causes BARC 209 to cross-link. In most embodiments, baking 113 is at a temperature in the range from 100° C. to 500° C. Cross-linking strengthens BARC 209 and prepares it for CMP.

Processing 110 continues with act 115, CMP. In some embodiments, CMP 115 reduces the thickness of BARC 209 by from 200 to 2000 Å. In some embodiments, CMP 115 stops in the plane D1-D1′, which is within BARC 209 and above layers 207 as shown in FIG. 4. In some embodiments, CMP 115 stops in the plane D2-D2′ corresponding to the top of a layer 207 of a material to be recessed. In some embodiments, CMP 115 stops the plane D3-D3′ corresponding to a layer 205 within which process 100 recesses layers 207. In some embodiments, CMP 115 stops on a film having a thickness in the range from 5 Å to 300 Å.

CMP 115 provides device 200 with a highly planar upper surface 218. As such, it is generally desirable to lower the surface 218 by CMP 115 until a practical limit is reached. In some embodiment, that limit is avoiding damage to a layer 205 past which layers 207 are to be recessed. In some embodiments, that limit is avoiding damage to an underlying layer 203.

In some embodiments, CMP 115 provides a high selectivity between BARC 209 and a layer 207 that is being recessed. A high selectivity is in the range from 10:1 to 5000:1. High selectivity for BARC 209 in CMP 115 facilitates forming a highly planar surface 218.

In some embodiments, CMP 115 uses a slurry of metal oxide particles. In some embodiments, the slurry is a colloid. A colloid contains very small particles. Very small particles have a high surface to volume ratio, which facilitates chemical reaction. In some embodiments, the metal oxide is one of SiO₂, Al₂O₃, and CeO₂. In some embodiments, the metal oxide particles react with hydroxyl groups in BARC 209 in a dehydration reaction and become bound to BARC 209 through ether linkages. Reacting and bonding in this manner increases the selectivity of CMP 115 for removing BARC 209 and increases the polishing rate.

In some embodiments, CMP 115 uses a table rotation speed in the range from 30 to 110 rpm. In some embodiments, CMP 115 uses a downward force in the range from 0.5 to 5 psi. In some embodiments, CMP 115 uses a slurry flow rate in the range from 50 to 500 ml/min. These CMP conditions can facilitate forming a highly planar surface 218, maintaining the integrity of BARC 209 during CMP 115, and maintaining a high polishing rate.

Processing 110 continues with act 117, etching to recess BARC 209 to a target height 206B as shown in FIG. 5A and 5B. In some embodiments, etching 117 has a low selectivity between BARC 209 and a layer 207. A low selectivity (BARC 209 versus layer 207) is in the range from 1:5 to 10:1. In some embodiments, etching 117 has a very low selectivity between BARC 209 and a layer 207. A very low selectivity is in the range from 1:2 to 2:1. In some embodiments, etching 117 recesses BARC 209 and layers 207 to approximately the same extent, which is most desirable, and produces a structure as shown in FIG. 5A. In some embodiments, etching 117 recesses BARC 209 more than layers 207 and produces a structure as shown in FIG. 5B.

In most embodiments, etching 117 is dry etching. In some embodiments, etching 117 is plasma etching with source gases that include H₂ and N₂. In some the plasma etching is characterized in part by the absence of fluorine compounds from the source gases. In some embodiments, etching 117 uses a flow rate for the source gases that is in the range from 5 to 1000 ml/min. In some embodiments, etching 117 is carried out at a pressure in the range from 1 to 100 mTorr. In some embodiments, etching 117 uses a plasma source at a power setting in the range from 200 to 5000 W. In some embodiments, etching 117 uses bias power up to 500 W. In some embodiments, etching 117 is carried out with substrate 201 at a temperature in the range from 10 to 60° C. Plasma etching using conditions within these parameters can provide a low selectivity etch that progresses at suitably high rate.

In some embodiments, etching 117 reduces the thickness of BARC 209 by from 10 to 3000 Å. In some embodiments, target height 206B corresponds to the height of a layer 203 underlying one or more of the layers 207. In some embodiments, target height 206B corresponds to recessing layers 207 a distance 216 within layer 205. The combination of CMP 115 to provide a highly planar surface 218 followed by low selectivity etching 117 causes BARC 209 to be uniformly recessed to the plane B-B′. Portions of BARC 209 significantly above the plane B-B′ are effectively removed. Portions of BARC 209 and other materials forming parts of device 200 that are significantly below the plane B-B′ are left intact. In some embodiments, etching 117 also causes layers 207 to be uniformly recessed to a plane.

Processing 110 optionally continues with further processing to recess layers 107. These options are relevant for results as shown in FIG. 5B and are identified with decision 118. In some embodiments where additional removal is desired, process 110 continues with act 120. Act 120 is selective etching where the selectivity is for removing layers 107 over BARC 209 to produce a structure as shown in FIG. 5A. For etching 120, BARC 209 masks structures below the plane B-B′.

In some embodiments where additional removal is desired, process 110 continues by repeating acts 111 through 117. In these embodiments, with each repetition layer 207 a become further recessed and more uniformly recessed. The resulting structure progresses from the form of FIG. 5B toward the form of FIG. 5A.

In some embodiments, processing 110 continues with act 119, removing BARC 209 to produces a structure as shown in FIG. 6. Act 119 is optional. In some embodiments, removal of BARC 209 is postponed. BARC 209 can be removed by any suitable dry or wet etching process.

BARC 209 can stabilize the surface of device 200 and exclude contaminants from gaps 208 during CMP 115 and etching 117. BARC 209 can uniformly recess under etching 117 to form a mask having a planar upper surface for etching 120. BARC 209 is a relatively hard material that facilitates maintaining a planar upper surface of device 200 during CMP 115.

As the term is used herein, a bottom anti-reflective coating (BARC) is a material recognized in the IC device manufacturing industry as a BARC, a highly cross-linking organic polymer that is functional as a BARC for photolithography, or a highly cross-linking organic polymer that has similar hardness and etch susceptibilities to organic polymers known in the industry as BARCs. In some embodiments, BARC 209 is a material known in the industry as a bottom anti-reflective coating. In some embodiments, BARC 209 is a material sold in a form suitable for spin coating onto wafers. In some embodiments, BARC 209 is a material that is functional as a bottom anti-reflective coating in photolithography. In some embodiments, BARC 209 is an organic polymer or copolymer. In some embodiments, BARC 209 is susceptible to a high degree of cross-linking.

In some embodiments, BARC 209 includes monomer units having hydroxyl groups. In some embodiments, BARC 209 includes monomer units that undergo hydration when exposed to water at a suitable pH. Unsaturated hydrocarbons are generally susceptible to hydration. In some embodiments, BARC 209 includes monomer units that have alkenes, alkynes, or aromatic groups. In some embodiments, BARC 209 includes ester, acrylate, or isocyanate monomers. In some embodiments, BARC 209 is an acrylate polymer or copolymer. In some embodiments, BARC 209 includes an aromatic monomer. In some embodiments, BARC 209 is a styrene polymer or copolymer. A BARC 209 having hydroxyl groups, or capable of acquiring hydroxyl groups through a hydration reaction, can react with oxide abrasive particles in a dehydration reaction that binds BARC 209 to the abrasive particles through ether linkages during CMP 115.

In some embodiments, process 100 is a hard mask removal process. In some embodiments, the hard mask removal processes removes a hard mask used to pattern gates from a dummy gate stack. FIG. 7 provides an example, which is a process 100A in accordance with some embodiments of the present disclosure. FIGS. 8-13 illustrate an example integrated circuit device 200A undergoing process 100A. Process 100A includes a series of acts 101A that form a topographically variable hard mask 219 and a series of acts 110A, which is an embodiment of the previously described BARC-assisted etch back 110.

The series of acts 101A includes act 121, forming a dummy gate stack 204 over a substrate 201, act 123 forming a hard mask 219 over dummy gate stack 204, and act 125, pattering hard mask 219 to provide a structure as shown in FIG. 8. Although FIGS. 8-13 show process 100A being used to form dummy gates for conventional transistors, in some embodiments process 100A is used to form dummy gates for finFETs. As shown in FIG. 8, dummy gate stack 204 includes a layer 217 of sacrificial material. In some embodiments, the sacrificial material is polysilicon. In some embodiments, dummy gate stack 204 includes a high-k dielectric layer 213. In some embodiments, hard mask 219 is formed with a thickness in the range from 500 to 9000 Å. In some embodiments, hard mask 219 is one of SiO₂, SiN, SiC, SiCN, SiON, SiOCN, or a combination thereof. In some of these embodiments, hard mask 219 is one of SiO₂, SiN, and SiCN, which are particularly useful as hard mask materials.

The series of acts 101A continues with act 127, patterning dummy gate stack 204 to form dummy gates 229, act 129, forming spacers 215, and act 131, forming source/drain regions 211 as shown in FIG. 9. In some embodiments, source/drain regions 211 are formed by ion implantation. In some embodiments, source/drain regions 211 are raised source/drain regions formed by epitaxy.

As shown in FIG. 9, acts 127 through 131 reduce the thickness 210 of hard mask 219. In some embodiments, acts 127 through 131 thin hard mask 219 until its maximum thickness 210A is in the range from 50 to 2000 Å less than its initial thickness 210. Acts 127 through 131 also cause thickness 210 of hard mask 210 to vary across substrate 201 between a maximum thickness 210A and a minimum thickness 210B. These variations stem from variations in the channel lengths 220 of dummy gates 229 and from variation in the pattern density of dummy gates 229 across substrate 201. Hard mask 219 is thinner in regions 202B as compared to regions 202A because the mean channel length 220 is shorter in regions 202A and because the fraction of substrate 201's area that is covered by hard mask 219 is lower in region 202B. In some embodiments, processing 101A causes hard mask 219 to have a variation in the range from 50 to 2000 Å between its maximum thickness 210A and its minimum thickness 210B.

Process 100A continues with a series of acts 110A, which are an embodiment of BARC-assisted etch back 110 including at least acts 111-117 shown in FIG. 1. In processing 110A, act 111 forms BARC 209 as shown in FIG. 10. In some embodiments of processing 110A, the thickness of BARC 209 is in the range from 500 to 5000 Å. Processing 110A includes baking 113. In some embodiments of processing 110A, baking 113 is baking at a temperature in the range from 150 to 300° C.

In processing 110A, CMP 115 reduces the height of BARC 209 as shown in FIG. 11. In some embodiments of processing 110A, CMP 115 lowers the height of BARC 209 by from 500 to 2000 Å. In some embodiments of processing 110A, CMP 115 stops on hard mask 219 as shown in FIG. 11. In some other embodiments of processing 110A, CMP 115 stops in BARC 209 just above the height of hard mask 219.

In processing 110A, etching 117 further reduces the height of BARC 209. In some embodiments, etching 117 removes hard mask 219 from sacrificial layer 217 as shown in FIG. 12. In some embodiments, hard mask 219 is removed from sacrificial layer 217 by further processing as indicated by decision 118 in FIG. 1. In some embodiments of processing 110A, etching 117 reduces the height of BARC 209 by from 50 to 3000 Å. In some embodiments of processing 110A, etching 117 takes places with substrate 201 at a temperature in the range from 20 to 40° C. In some embodiments of processing 110A, etching 117 is characterized in part by the absence of CF₄ from plasma source gases. Plasma etching with CF₄ can damage polysilicon, which can be the material used for sacrificial layer 217.

Processing 110A removes hard mask 219 while preserving the height 214 of dummy gates 229. In some embodiments, the height 214B of dummy gates 229 after processing 110A is at least 90% the height 214A of dummy gates 229 before processing 110A. In some embodiments, the height 214B of dummy gates 229 varies by 10% or less among dummy gates 229 after processing 110A.

In some embodiments, process 100 is a replacement gate process. FIG. 14 provides an example of a replacement gate process 100B in accordance with some embodiments of the present disclosure. FIGS. 15-39 illustrate an example IC device 200B undergoing process 100B. In some embodiments, IC device 100B includes tri-gate or gate-all-around finFETs. Process 100B begins with act 133, forming fins 247 on a semiconductor substrate 201 and act 135, forming a first inter-level dielectric (ILD) layer 243 as shown in FIG. 15. Semiconductor substrate 201 can be any suitable type of substrate. In some embodiments, substrate 201 is a semiconductor wafer. In some embodiments, substrate 201 is semiconductor-on-insulator.

Fins 247 include n-channel fins 247A and 247B and p-channel fins 247C and 247D. FIG. 15 illustrates n-channel fins 247A and 247B formed in a p-well 245A and p-channel fins 247C and 247D formed in an n-well 245B, however, fins 247 can be formed and doped in any suitable manner. In some embodiments, fins 247 are etched from substrate 201. In some embodiments, fins 247 are replacement fins produced by epitaxial growth. In some embodiments, fins 247 are etched from doped substrate 201. In some embodiments, fins 247 are grown with dopants. In some embodiments, fins 247 are doped after their formation. In some embodiments, fins 247 have a height in the range from 100 to 1000 Å.

ILD layer 243 can be formed by any suitable process. In some embodiments, ILD layer 243 is formed by depositing dielectric over fins 247, chemical mechanical polishing to the height of fins 247, then etching to recess ILD layer 243 as shown in FIG. 15. In a replacement fin process, ILD layer 243 can form a matrix in which fins 247 are grown, after which ILD layer 243 is recessed. ILD layer 243 can be formed of any suitable dielectric or combination of dielectric. Dielectrics that can be suitable include SiO₂, silicate glasses, and low-k dielectrics.

Process 100B continues with a series of acts 100A by which dummy gates 229, spacers 215, and source/drain regions 211 are formed. In some embodiments, these acts are an embodiment of process 100A of FIG. 7. FIGS. 16 and 16A show an intermediate stage of this process following the formation of spacers 215.

FIG. 16A provides a perspective view of portion 232 of FIG. 16. With the exception of FIG. 16A, FIGS. 15-39 are cross-sectional views along a plane 230, which is shown in FIG. 16A. Plane 230 runs perpendicular to fins 247, cuts fins 247 mid-channel, and runs along the lengths of dummy gates 229. Source/drain regions 211 are formed at locations 234, identified in FIG. 16A, which are outside these views. At the conclusion of acts 100A, hard mask 219 is removed as shown in FIG. 17.

Process 100B continues with act 139, forming a contact etch stop layer (CESL) 221 and act 141, forming an additional inter-level dielectric layer 223 as shown in FIG. 18. In some embodiments, CESL 221 is SiN. Act 143 is chemical mechanical polishing to expose an upper surface 236 of dummy gates 229 as shown in FIG. 19. Process 100B continues with act 145, dummy gate removal to form trenches 212, act 147, forming an interfacial (IL) layer (not shown), and act 149, forming a high-k dielectric layer 213 as shown in FIG. 20. It should be appreciated that the IL layer and high-k dielectric layer 213 can be formed with dummy gate stack 204 or formed subsequently as in this example.

Process 100B continues with a series of acts 101B that form topographically variable metal layers, including work function metal layers 237 that are to be subsequently recessed within ILD layer 223. The individual and collective thicknesses of these metals will vary between standard voltage and low voltage transistors and between n-channel and p-channel transistors. In some embodiments, these variable thicknesses result from a plurality of deposition, masking, and etching operations as shown in this example. In some embodiments, p-channel work function metals 237 are deposited before n-channel work function metals 237 as shown in FIGS. 21-27. In some embodiments, n-channel work function metals 237 are deposited before p-channel work function metals 237. Some or all of these work function metals 237 can be recessed by BARC-assisted etch back 100B.

Process 101B begins with act 151, forming capping and barrier metal layers 239 and act 155, forming a first work function metal (WFM1) layer 237A as shown in FIG. 21. WFM1 layer 237A lines trenches 212 and rises to the tops and above trenches 212. In some embodiments capping and barrier metal layers 239 include a TiN capping layer. In some embodiments, capping and barrier metal layers 239 include a TaN barrier metal layer. Examples of work function metals include, without limitation, Ti, TiN, TiAl, W, TaN, WN, Re, Ir, Ru, and Mo. In some embodiments, a work function metal is one of Ti, TiN, TiAl, and TaN.

Process 101B continues with act 157, forming a first gate metal mask 235A as shown in FIG. 22. Mask 235A masks n-channel fins 247 and some of the p-channel fins 247. Act 159 is an etch process that removes WFM1 layer 237A from the exposed p-channel fins 247 as shown in FIG. 23. Mask 235A is then stripped.

Process 101B continues with act 161, forming a second work function metal (WFM2) layer 237B as shown in FIG. 24. Act 163 then forms a second gate metal mask 235B that covers n-channel fins 247 as shown in FIG. 25. Act 165 is an etch process that removes WFM2 layer 237B from the p-channel fins 247 as shown in FIG. 26. Etch process 165 is a selective etch that removes exposed portions of WFM2 layer 237B while leaving at least some thickness of the exposed portions of WFM1 layer 237A intact. Mask 235B is then stripped.

Process 101B continues with act 167, forming a third work function metal (WFM3) layer 237C as shown in FIG. 27. To avoid current leaks, WFM layers 237 are to be removed from over ILD layer 223 and recessed from an upper surface 228 of ILD layer 223. The overall thickness of WFM layers 237 varies across substrate 201. In some embodiments, the difference between the minimum and the maximum thickness of WFM layers 237 is in the range from 100 to 500 Å. This variation in thickness and the variation in pattern density of WFM layers 237 across substrate 201 are challenges to performing a planar recessing process. In process 100B, those challenges are met by applying BARC-assisted etch back 100B, which is an embodiment of BARC-assisted etch back 110 of FIG. 1.

Processing 110B begins with act 111, forming a coating of BARC 209 as shown in FIG. 28 and act 114, baking. In some embodiments of processing 110B, the coating thickness of BARC 209 is in the range from 300 to 3000 Å. In some embodiments of processing 110B, baking 114 is baking at a temperature in the range from 150 to 250° C.

In processing 110B, act 115, CMP, reduces the height of BARC 209 as shown in FIG. 29. In some embodiments of processing 110B, CMP 115 lowers the height of BARC 209 by an amount in the range from 500 to 2000 Å. In some embodiments of processing 110B, CMP 115 stops on WFM layers 237 as shown in FIG. 29. In some embodiments of processing 110B, CMP 115 stops in BARC 209 just above the height of WFM layers 237. In some embodiments of processing 110B, CMP 115 stops on CESL 221 or spacers 215. In some embodiments of processing 110B, CMP 115 stops on ILD layer 223.

In processing 110B, act 117, etching back, further reduces the height of BARC 209 and recesses BARC 209 within ILD layer 223. In some embodiments, etching 117 also recesses one or more of WFM layers 237 as shown in FIG. 30. In some embodiments, etching 117 also recesses capping and barrier metal layers 239. In some embodiments of processing 110B, one or more of WFM layers 237 are recessed by further processing as indicated by decision 118 in FIG. 1. In some embodiments of processing 110B, etching 117 reduces the height of BARC 209 and WFM layers 237 by an amount in the range from 10 to 1000 Å. In some embodiments of processing 110B, etching 117 takes places with substrate 201 at a temperature in the range from 20 to 40° C. In some embodiments of processing 110B, etching 117 is characterized in part by the absence of CF₄ from plasma source gases. CF₄ present during plasma etching 117 can react with metals in WFM layers 237 to produce byproducts that act as an etch stop layer and interfere with recessing of WFM layers 237.

In some embodiments, BARC 209 is stripped at the conclusion of processing 110B. In some other embodiments, as shown by this example, BARC 209 is further used to assist in forming a mask for an additional work function metal etch. In some alternative embodiments, this additional work function metal etch is carried out in a BARC-assisted etch back 100B that includes selective etch 120.

In FIG. 14, BARC-assisted etch back 100B is followed by act 171, which is forming a third gate mask 235C as shown in FIG. 31. Mask 235C masks p-channel fins 247 and some of the n-channel fins 247. Act 173 is an etch process that removes BARC 209 from the exposed n-channel fins 247 as shown in FIG. 32. In some embodiments, act 173 is followed immediately by act 175, which an etch process that removes WFM layers 237 from the exposed n-channel fins 247 as shown in FIG. 33.

In some alternate embodiments, mask 235C is stripped before act 175 as shown in FIG. 32A. Moreover, acts 171 and 173 can occur after etching 117 within processing 110B. Then, act 175, the etch process that removes WFM layers 237 from the exposed n-channel fins 247, can also be a selective etch 120 that recesses WFM layers 237. In these embodiments, BARC 209 masks WFM layers 237 below the target removal height everywhere but locations where it is desirable to remove WFM layers 237 entirely. In these alternate embodiments, the etch 175 that removes WFM layers 237 from the exposed n-channel fins 247 is combined with an etch 120 that recesses WFM layers 237, thereby reducing the required number of etch operations. In other embodiments mask 235C is stripped after act 175

Process 100B continues with act 177, removing the remaining portion of BARC to produce a structure as shown in FIG. 34, then act 179, depositing a metal 227 that fills trenches 212 as shown in FIG. 35. Metal 227 can be any suitable metal. Examples of metals that can be suitable include Al, W, Co, Cu, and Ni. Act 181 is a CMP process that lowers metal 227 to the height of ILD layer 223 as shown in FIG. 36. Act 183 is an etch process that recesses metal 227 within ILD layer 223 as shown in FIG. 37. In some embodiments, one or more of WFM metals 237 is recessed together with metal 227 in act 183. In some embodiments, capping and barrier metal layers 239 are recessed together with metal 227 in act 183. However, in some embodiments one or more of WFM metals 237 and capping and barrier metal layers 239 cannot be recessed effectively together with metal 227 in act 183. In these embodiments, at least the layers that cannot be recessed effectively together with metal 227 in act 183 are recessed by processing BARC-assisted etch back 100B.

Process 100B continues with act 185 deposits a third ILD layer 225 as shown in FIG. 36. Act 187 is a CMP process that lowers ILD layer 225 to the same height as ILD layer 223 as shown in FIG. 39. As shown in FIG. 39, the thickness 238 of ILD layer 223 is generally determined by the extent to which metal 227 is recessed by etching 183. In some embodiments, thickness 238 is in the range from 10 to 1000 Å. In some embodiments, thickness 238 is in the range from 50% to 95% the height 244 of ILD layer 223 over WFM layers 237 where they lie mid-channel over fins 247. Making thickness 238 over half the height 244 provides a desirable amount of insulation, but the process window is relatively narrow.

In some embodiments, BARC-assisted etch back 100B recesses one or more WFM layers 237 to an equal or greater extent than etching 183 recesses metal 227. This results in WFM layers 237 being below the upper surface of metal 227. In most embodiments, BARC-assisted etch back 100B does not reduce the thickness 240 of any of WFM layers 237 where they lie mid-channel over fins 247. BARC-assisted etch back 110B can recess WFM layers 237 to within the limits of these parameters.

The present disclosure provides a method of manufacturing an integrated circuit device that includes processing a semiconductor substrate through a series of operations that form a topographically variable surface including a layer of a material on the surface. The layer of the material varies in height across the substrate. Spin coating forms a polymeric bottom anti-reflective coating (BARC) over the surface. Baking induces cross-linking in the BARC. CMP removes a first portion of the BARC. Etching then removes a second portion of the BARC and effectuates a top-down recessing of the BARC. In some embodiments, the etching has a low selectivity between the BARC and the layer that varies in height. In some embodiments, the etching that removes a second portion of the BARC simultaneously reduces the height of the layer and effectuates a top-down recessing of the layer.

The methods provided by the present disclosure effectuate a planar recessing of a material layer that, at least initially, is variable in height. Any of the material layer above a certain height can be removed. Structures that are substantially below that certain height can be protected from contamination and left intact. The method can be particularly effective when an abrasive used during CMP forms ester linkages with the BARC.

The present disclosure also provides a method of manufacturing an integrated circuit device that includes forming a dummy gate stack on a semiconductor substrate, forming a hard mask over the dummy gate stack, patterning the dummy gate stack using the hard mask to form dummy gates, forming spacers adjacent the dummy gates, and forming sources and drains aligned to the spacers. The hard mask is then removed by depositing a bottom anti-reflective coating over the dummy gates, chemical-mechanical polishing to form a planar upper surface that includes a surface of the bottom anti-reflective coating, and plasma etching the chemically-mechanically polished surface to recess the BARC to approximately the height of the dummy gates, and removing the hard mask before removing the BARC. In some embodiments, the etching that recesses the BARC to approximately the height of the dummy gates also removes the hard mask.

The present disclosure further provides a method of manufacturing an integrated circuit device including a replacement gate process. The method includes forming finFETs having dummy gates having a height and wrapping fins on a semiconductor substrate, forming a first dielectric layer that covers the semiconductor substrate, removing the dummy gates to form trenches, and forming a layer of a work function metal over a channel region of some of the fins. The layer of the work function metal lines at least a portion of the length of at least some of the trenches and rises to the tops of the trenches at some locations. The layer of the work function is then recessed by depositing a polymeric bottom anti-reflective coating, baking to crosslink the bottom anti-reflective coating, chemical-mechanical polishing to form a planar upper surface comprising the bottom anti-reflective coating, and after the chemical-mechanical polishing, plasma etching. The plasma etching causes the BARC to become recessed within the trenches. In some embodiments, the plasma etching also reduces the height reached by the layer of the work function metal and causes the layer of the work function metal to become recessed within the trenches. The process can prevent the work function metal from causing shorts through a dielectric layer that will subsequently be formed in the upper part of the trenches to insulate the gate electrodes from overlying structures.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of manufacturing an integrated circuit device, comprising: processing a semiconductor substrate through a series of operations to form a topographically variable surface including a layer of a material on the surface, wherein the layer varies in height across the substrate; spin coating a polymeric bottom anti-reflective coating (BARC) over the surface; inducing cross-linking in the BARC by baking; chemically mechanically polishing to remove a first portion of the BARC; and etching to effectuate a top-down recessing of the BARC.
 2. The method of claim 1, wherein the etching to effectuate a top-down recessing of the BARC is etching with a low selectivity between the BARC and the material and effectuates a top-down recessing of the layer of the material.
 3. The method of claim 1, wherein the chemical mechanical polishing stops on the layer of the material.
 4. The method of claim 2, wherein the etching recesses the BARC and the layer of the material within a dielectric layer on the surface.
 5. The method of claim 2, wherein the spin coating, the chemical mechanical polishing, and the etching with a low selectivity take place within and form part of a replacement gate process.
 6. The method of claim 1, wherein the layer of the material is a layer of a hard mask.
 7. The method of claim 1, wherein the layer of the material is a work function metal that forms part of a metal gate electrode.
 8. The method of claim 7, wherein the metal gate electrode is formed over one or more finFET fins.
 9. The method of claim 1, wherein the chemical mechanical polishing comprises polishing with a slurry comprising abrasive particles comprising a material selected from the group consisting of SiO₂, Al₂O₃, and CeO₂.
 10. The method of claim 1, wherein the abrasive particles form chemical bonds with the BARC material during the chemical mechanical polishing process.
 11. The method of claim 10, wherein the abrasive particles bond to hydroxyl groups of the BARC material.
 12. The method of claim 1, further comprising: after the etching to effectuate a top-down recessing of the BARC, etching with a high selectivity between the material and the BARC to recess the layer of the material.
 13. A method of manufacturing an integrated circuit device, comprising: forming a dummy gate stack over a semiconductor substrate; forming a hard mask over the dummy gate stack; patterning the dummy gate stack using the hard mask to form dummy gates; forming spacers adjacent the dummy gates; forming sources and drains aligned to the spacers; forming a polymeric bottom anti-reflective coating (BARC) over the dummy gates, wherein the BARC fills gaps between the dummy gates; baking the BARC; chemically mechanically polishing to form a planar upper surface comprising the BARC; plasma etching the chemically-mechanically polished surface, wherein the plasma etching recesses the BARC to approximately the height of the dummy gates; and removing the hard mask before removing the BARC.
 14. The method of claim 13, wherein the chemical-mechanical polishing stops on the hard mask.
 15. The method of claim 13, wherein the plasma etching of the chemically-mechanically polished surface removes the hard mask.
 16. The method of claim 13, wherein the plasma etching of the chemically-mechanically polished surface has a low selectivity between the bottom anti-reflective coating and the hard mask.
 17. A method of manufacturing an integrated circuit device, comprising: forming finFETs having dummy gates having a height and wrapping fins on a semiconductor substrate; forming a first dielectric layer that covers the semiconductor substrate and has a height at least equal to the height of the dummy gates; removing the dummy gates to form trenches that are within the first dielectric layer; forming a layer of a work function metal over a channel region of some of the fins, wherein the layer of the work function metal lines at least a portion of the length of at least some of the trenches, whereby the layer of the work function metal rises to the tops of the trenches at some locations; forming a polymeric bottom anti-reflective coating (BARC), wherein the BARC lies above the layer of the work function metal and fills the trenches; baking the BARC; chemically mechanically polishing to form a planar upper surface comprising the BARC; and after the chemical-mechanical polishing, plasma etching, wherein the plasma etching causes the BARC to become recessed within the trenches.
 18. The method of claim 17, further comprising: removing the BARC; filling the trenches with metal; recessing the metal within the trenches; filling the trenches with additional dielectric; and chemically mechanically polishing to make the additional dielectric approximately the same height as the first dielectric layer.
 19. The method of claim 18, wherein the plasma etching has a low selectivity between the BARC and the work function metal, reduces the height reached by the layer of the work function metal, and causes the layer of the work function metal to become recessed within the trenches.
 20. The method of claim 17, further comprising: forming a mask over the recessed BARC; etching to remove the BARC where it is exposed through the mask, wherein the etching removes the BARC from over some of the fins; plasma etching to remove the layer of the work function metal from over the fins from which the BARC was removed; and removing a remaining portion of the BARC. 